1. Field of the Invention
The invention generally relates to heating systems for ovens, particularly gas heating systems.
2. Description of the Relevant Art
In the field of gas burners for ovens, the ovens are used in large commercial or institutional kitchens.
The energy produced by the combustion is recovered in thermal form. The products of the gas combustion pass through, for example, heat exchanger tubes where they are cooled to remove the thermal energy therefrom. Apart from possible pressure losses in the heat exchanger tubes or in chimney flues, the combustion gases from the burner are substantially at atmospheric pressure. The mechanical energy of the combustion gases from the burner is a drawback, causing vibrations and noise in the oven.
A gas cooker fitted with hollow heating elements passed through by combustion products from a gas burner is known. One drawback of this type of burner is the limited thermal power. More specifically, when the flow of the mixture of air and inflammable gas increases, the propagation speed of the combustion of the flame in the gas mixture flow may be lower than the speed of the flow of the mixture and the flame blows off the burner. If the phenomenon is not rapidly corrected, the flame is blown out and extinguished. Conversely, if the gas mixture flow is lower than the propagation of the flame, said flame may go upstream of the burner. A further drawback of this type of oven is that under the effect of the thermal variations and the mechanical effects of the combustion gas flow, the heating elements, brought to a high temperature, may start to vibrate. This causes an unpleasant noise and reduces the lifespan of the oven.
A flame retention plate is known for a gas burner. This plate plays the role of a distribution screen for the gas mixture streams. It comprises a compressed network of interwoven threads. This structure allows gas streams to pass in a substantially evenly distributed manner over the entire surface of the plate and a uniform distribution of the flame produced. However, this type of burner has the drawback of being restricted in the thermal output per cm2 of the retention plate. Moreover, this type of burner aims to produce flames of relatively low height and where the thermal output is localised close to the retention plate. It is apparent that this type of burner is suitable for heating, from the outside, water coils for domestic boilers, for example. For ovens, it is desirable to heat the heat exchanger tubes from the inside. It is desirable to distribute the flame to reduce hot spots.
A flame retention device is known, comprising several identical rings composed of a compressed network of interwoven metal threads. The gas mixture passes through the rings in a radial manner. Each of the rings produces a radial circular flame. The rings are coaxial and superposed over one another and separated by solid crosspieces, which are not passed through by the gas mixture. The external diameter of the solid crosspieces is less than the external diameter of the rings of the compressed network. Pilot flames are formed in the grooves corresponding to the crosspieces. The aforementioned drawback, namely that of increasing thermal energy solely at the point of the retention plate of the burner, is accentuated here, as the combustion gases are propagated radially relative to the axis of the burner.
A burner provided with porous tubular body elements is known. The wall of the tube is made of a compressed network of threads. A plurality of tubular shapes are axially nested in one another to form a burner of larger dimensions. The stabilisation of the flame is improved by a deflector plate. In this type of burner, the thermal energy is released radially relative to the axis of the burner.
A burner head has been disclosed where a sealed combustion chamber opens into a plurality of heat exchanger tubes passed through by the combustion gases. A housing surrounding the combustion chamber brings fresh air to the heat exchanger tube inlet to reduce the temperature of the transition between the combustion chamber and the heat exchanger tubes. In this type of burner, the air contributing to the combustion of the inflammable gas is entirely contained in the gas mixture upstream of the combustion chamber. The combustion products are discharged through heat exchanger tubes by an outlet manifold. The drawback with this type of burner is that, for limiting the combustion products which are not oxidised by combustion, it is necessary to introduce into the gas mixture, which passes through the burner, excess air relative to the stoichiometric proportions of the gas. For a given thermal output of the burner, the over-supply of air may cause a detachment of the flame. Even if the detachment of the flame is limited, however, the over-supply of air reduces the thermal output of the flame.
A need exists for a burner for a gas oven which alleviates the aforementioned drawbacks and, in particular, which allows the thermal energy of the burner to be increased, by avoiding the detachment of the flame and by distributing said flame.